Constant-current output driver with reduced over-shoot

ABSTRACT

A constant-current FET functions as a constant current element by application of a constant voltage to the gate thereof. A first switch FET is disposed between the constant-current FET and a power supply without another switching element being disposed between the constant current FET and an output terminal. A second switch FET that performs an on/off operation in association with an on/off operation performed by the first switch FET is connected between the output terminal and ground.

BACKGROUND OF THE INVENTION

The present invention relates to a constant current output driver, forexample, a constant current output driver for emitting a light from alight emitting element such as an organic EL (electro luminescent)panel.

A light emitting diode (LED) and an organic EL (also called “organicLED”) has widely been spread as an image source in a display unit suchas a direct-view display unit or a virtual image display unit since ahigh visibility is obtained because the light emitting diode and theorganic EL per se emit a relatively large amount of high-luminancelight, and a display speed is higher than that of a TFT (thin filmtransistor) liquid crystal or the like to make it difficult to produce alatent image. Since the display panel using those LED or organic EL isof the current driven type, a constant current output driver is employedin the drive device.

FIG. 22 shows the structure of a conventional display device using theorganic EL of this type.

As shown in FIG. 22, the organic EL display unit includes an organic ELpanel 1, a scanning circuit 2, a drive circuit 3 and a not-shown lightemission control circuit that controls the switching operation of thescanning circuit 2 and the drive circuit 3.

The organic EL panel 1 includes anode lines A1 to Am and cathode linesB1 to Bn which are arranged in a simple matrix (lattice), and organic ELelements E11 to Emn connected to the respective intersecting positionsof the anode lines and the cathode lines which are arranged in the formof a lattice. The cathode lines B1 to Bn are connected to a scanningcircuit 51, and the anode lines A1 to Am are connected to the drivecircuit 3.

The scanning circuit 2 includes switches S21 to S2 n and conductsscanning operation by sequentially setting the cathode lines B1 to Bn tothe earth potential (0 V) while those switches S21 to S2 n sequentiallychange over to the earth terminal side at given time intervals.

The drive circuit 3 includes switches S31 to S3 m and constant currentelements C31 to C2 m connected to a power supply VDD. The drive circuit3 is so designed as to connect the anode lines A1 to Am to the constantcurrent elements C31 to C3 m while controlling the on/off operation ofthe respective switches S31 to S3 m in synchronism with the scanningoperation of the cathode line scanning circuit 2 and to supply a drivecurrent to the organic EL at a desired intersecting position, to therebyemit a light.

A case in which the cathode lines are scanned and the anode lines aredriven is shown in FIG. 22. The same effect is obtained in the structurein which the anode lines are scanned and the cathode lines are driven.

Now, it is assumed that the switch S22 in the scanning circuit 2 isconnected to the earth side to scan a row of the cathode line B2. Atthis timing, when the switches S31 and S33 in the drive circuit 3 arechanged over to the constant current elements C31 and C33 side (turnon), currents I12 and I13 flow in the light emitting elements E12 andE32 to emit a light.

An inverse bias voltage VCC identical in potential with the supplyvoltage is applied to other cathode lines B1 and B3 to Bn other than thecathode line B2 which is being scanned, to thereby prevent an error inlight emission.

The organic EL is made to emit a light at an arbitrary position byrepeating the scanning of the cathode lines B1 to Bn and the driving ofthe anode lines A1 to Am at a high speed, and display is made so thatthe respective organic ELs emit a light on the entire screen at the sametime.

In this situation, in order to prevent the amount of light emission frombeing made ununiform due to a difference between the current values thatflow in the respective organic ELs which is caused by a difference inthe wiring distance between the organic ELs, the respective anode linesA1 to Am are connected to the constant current elements C31 to C3 m thatfunction as the constant current source through the switches S31 to S3m.

FIG. 23 shows the unknown structure proposed in a case where theconventional constant current output driver made up of the constantcurrent elements of the above type and the switches that connect anddisconnect the constant current elements and the anode lines is formedof the enhancement MOSFET (metal oxide field effect transistor).

As shown in FIG. 23, the constant current output driver is designed suchthat a p-channel MOSFET 4 that functions as the constant currentelement, and a p-channel MOSFET 5 and an n-channel MOSFET 6 whichfunction as the switching elements are connected in series. The supplyvoltage VDD is applied to the drain of the MOSFET 4, and a voltage VGCwhich is always constant is applied to the gate of the MOSFET 4 in orderto output a constant current.

An input terminal IN is connected to both the gates of the MOSFETs 5 and6, an output terminal OUT is connected to the source of the MOSFET 5 andthe drain of the MOSFET 6, and the anode lines of the organic EL panelare connected to the output terminal OUT.

In the constant current output driver made up of the MOSFETs asdescribed above, when a switching signal which is supplied to the inputterminal changes from on (high level) to off (low level), the MOSFET 6changes from on to off and the MOSFET 5 changes from off to on. As aresult, the output terminal OUT which has been connected to the groundis connected to the MOSFET 4 which functions as the constant currentelement through the MOSFET 5 to output a constant current.

FIG. 25 shows the structure of a display unit using organic ELS forcolor display.

As shown in FIG. 25, in an organic EL panel 1 for color display, threetimes as many anode lines A1 to As (s=3m) as in a monochrome display aredisposed, and anode terminals Al to As for connection to the drivecircuit are disposed.

In the organic EL panel 1 for color display, organic ELs for red (R) areconnected at the intersecting positions of anode lines A1, A4, . . .As−2 and the respective cathode lines B1 to Bn, organic ELs for green(G) are connected at the intersecting positions of anode lines A2, A5, .. . As−1 and the respective cathode lines B1 to Bn, and organic ELs forred (R) are connected at the intersecting positions of anode lines A3,A6, . . . As and the respective cathode lines B1 to Bn, as in FIG. 22although being not shown.

Those light emitting elements for R, G and B are different in optimumconstant current value, respectively, when emitting the light. For thatreason, as shown in FIG. 25, in the conventional drive circuit thatdrives the organic EL panel 1 for color display, there are used a drivecircuit 3R for R, a drive circuit 3G for G and a drive circuit 3B for B.Each of the drive circuits 3R, 3G and 3B includes m (s/3) constantcurrent output sections and m constant current output terminals O1 toOm.

As shown in FIG. 25, in order to drive the organic ELs for R which aredisposed at every three organic ELs, the respective output terminals O1to Om of the drive circuit 3R for R are connected with the anodeterminals A1, A4, . . . As−2 of the organic EL panel 1 for colordisplay. Likewise, the respective output terminals O1 to Om of the drivecircuit 3GR for G are connected with the anode terminals A2, A5, . . .As−12 of the organic EL panel 1 for color display, and the respectiveoutput terminals O1 to Om of the drive circuit 3B for B are connectedwith the anode terminals A3, A6, . . . As.

As described above, in the case where the conventional constant currentoutput driver is formed of MOSFETs as. shown in FIG. 23, the currentflowing in the respective organic EL elements can be made substantiallyconstant by use of the constant current element.

However, the conventional constant current output driver suffers fromthe following problems.

A first problem is that over-shoot occurs in the current outputted fromthe output terminal OUT of the conventional respective constant currentoutput drivers, and there actually exists a moment where a current equalto or more than a given current flows in the light emitting element.

FIG. 24 shows the simulation result of an output current in the constantcurrent output driver shown in FIG. 23. As shown in FIG. 24, a largecurrent indicated by an arrow A flows as soon as the constant currentoutput turns on, and a large current indicated by an arrow B flows assoon as the constant current output turns off.

The current indicated by the arrow A is that charges charged in thesource of the MOSFET 5 while the MOSFET 5 shown in FIG. 23 is off flowsin the output terminal as soon as the MOSFET 5 turns on. At the sametime, the current flows in the minus direction but is canceled by theabove current and does not appear in the figure. This current in theminus direction is that a high frequency component flows through thecapacitor of a gate insulating film because the gate voltage IN of theMOSFET 5 and the MOSFET 6 changes from VDD to the ground.

The current indicated by the arrow B is that a high frequency componentflows through the capacitor of the gate insulating film because the gatevoltage IN of the MOSFET 5 and the MOSFET 6 changes from the ground toVDD.

The current in the minus direction indicated by an arrow C is a currentresulting from discharging the charges stored in the capacity componentof the organic EL connected to the output terminal OUT to the ground,which is not abnormal.

A second problem is stated below.

In the case of driving the organic EL panel, because a wiring resistanceis large, the wiring resistance is largely different because of adifference in the wiring length due to the. position of the organic ELelements on the organic EL panel 1 shown in FIG. 22. Therefore, avoltage applied to the respective constant current elements is alsolargely different. As a result, a demand exits for the constant currentelement of the drive circuit 3 that the voltage dependency change of theoutput current value is very small. However, in the case where theconventional constant current output driver is formed of MOSFETs asshown in FIG. 23, in order to reduce the voltage dependency change ofthe output constant current value, it is necessary to increase the gatelength of the p-channel MOSFET 4 that functions as the constant currentelement with a problem that the IC chip size of the drive circuit 3increases.

A third problem is that if the MOSFET is employed as the constantcurrent element of the constant current output driver as shown in FIG.23, the switching noise adversely affects the gate potential of theMOSFET 4 that functions as the constant current element, and theconstant current value fluctuates. In the case where the organic ELpanel using a plurality of drivers is driven, because many noises arereceived at various timings, a larger problem is caused.

A fourth problem is stated below.

The MOSFET has a temperature characteristic that the output currentvalue changes in accordance with the temperature change. Also, thecurrent value outputted from the constant current FET 50 is nearlyproportional to the square of the gate voltage.

For that reason, if a constant voltage VGC is always applied to the gateG of the constant current FET 50 regardless of the temperature change,there arises such a problem that the output current largely changes inaccordance with the temperature change.

A fifth problem is stated below.

In the conventional constant current output driver in the case wherecolor display is conducted using the organic ELs, the m constant currentoutput sections that drive the light emitting elements for R aredisposed in the drive circuit 3R for R together, the m constant currentoutput sections that drive the light emitting elements for G aredisposed in the drive circuit 3R for G together, and the m constantcurrent output sections that drive the light emitting elements for B aredisposed in the drive circuit 3R for G together. On the other hand, therespective light emitting elements of the organic EL panel 1 for colordisplay and their anode terminals A1 to As are disposed in the order ofR, G and B.

For that reason, in the case where the drive circuit 3R for R, the drivecircuit 3G for G and the drive circuit 3B for B are connected to theorganic EL panel 1 for color display, because the wirings intersectswith each other as shown in FIG. 25, multi-layer wirings must beprovided, to thereby increase the costs.

Also, in the case where the organic EL panel 1 for color display ismounted on a COG (chip on glass), because it is extremely difficult toprovide the multi-layer wirings, the display device could not besubstantially mounted on the COG with the structure shown in FIG. 25.

The present invention has been made in order to solve theabove-described problems, and therefore an object of the presentinvention is to provide a constant current output driver which reducesthe occurrence of over-shoot at the first, which is extremely small inthe voltage dependency change of the output constant current value atthe second, which reduces the adverse affect of the switching noise onthe constant current property at the third, which reduces a change inthe output current value due to the temperature change at the fourth,and which can be connected to the light emitting element panel for colordisplay through single-layer wirings.

SUMMARY OF THE INVENTION

In the present invention as recited in claim 1, as conceptually shown inFIG. 1, the above object is achieved by the provision of a constantcurrent output driver for emitting a light from a light emitting elementby supplying a constant current, the constant current output drivercomprising: a constant current output element that outputs a constantcurrent (100); a first switching element (101) disposed between theconstant current output element and a power supply (VDD), forelectrically connecting and disconnecting the power supply and theconstant current output element; and a first output terminal (102)connected to a current output side of the constant current element withno switching element disposed therebetween.

In the present invention as recited in claim 2, as conceptually shown inFIG. 2, the above object is achieved by the provision of a constantcurrent output driver for emitting alight from a light emitting elementby supplying a constant current, the constant current output drivercomprising: a constant current output element (100) that outputs aconstant current; a first switching element (101) disposed between theconstant current output element and a power supply (VDD), forelectrically connecting and disconnecting the power supply and theconstant current output element; a second switching element (103)connected between current output side of the constant current outputelement and a second terminal (104), for performing an on/off operationin association with the on/off operation of the first switching element;and a first output terminal (102) connected between the current outputside of the constant current output element and the second switchingelement (103) with no switching element therebetween.

In the present invention as recited in claim 3, as conceptually shown inFIG. 3, the above object is achieved by the provision of a constantcurrent output driver comprising:

a first field effect transistor (50) for outputting a constant currentwith the application of a constant voltage (VGC) to a gate thereof;

a second field effect transistor (40) disposed between the first fieldeffect transistor and a power supply (VDD), for electrically connectingand disconnecting the power supply and the first field effecttransistor; and

A first output terminal (OUT) connected to a current output side of thefirst field effect transistor with no switching element therebetween.

In the present invention as recited in claim 4, as conceptually shown inFIG. 4, the above object is achieved by the provision of a constantcurrent output driver comprising: a first field effect transistor (50)for outputting a constant current with the application of a constantvoltage (VGC) to a gate thereof; a second field effect transistor (40)disposed between the first field effect transistor and a power supply(VDD), for electrically connecting and disconnecting the power supplyand the first field effect transistor; a third field effect transistor(70) connected in series with a current output side of the first fieldeffect transistor and having a gate thereof applied with a constantvoltage (VGC2) different from the constant voltage which is applied tothe gate of the first field effect transistor; and a first outputterminal (OUT) connected to a current output side of the third fieldeffect transistor through no switching element.

In the present invention as recited in claim 5, as conceptually shown inFIG. 5, the above object is achieved by the provision of a constantcurrent output driver comprising: a first field effect transistor (50)for outputting a constant current with the application of a constantvoltage (VGC) to a gate thereof; a second field effect transistor (40)disposed between the first field effect transistor and a power supply(VDD), for electrically connecting and disconnecting the power supplyand the first field effect transistor; a third field effect transistor(60) forming a channel different from that of the second field effecttransistor, connected between a current output side of the first fieldeffect transistor and a second terminal (a terminal to which the groundis connected), and having a gate thereof commonly connected to an inputterminal (IN) together with a gate of the second field effecttransistor; and a first output terminal (OUT) connected between acurrent output side of the first field effect transistor and the thirdfield effect transistor through no switching element.

In the present invention as recited in claim 6, as conceptually shown inFIG. 7, the above object is achieved by the provision of a constantcurrent output driver comprising: a first field effect transistor (50)for outputting a constant current with the application of a constantvoltage (VGC) to a gate thereof; a second field effect transistor (40)disposed between the first field effect transistor and a power supply(VDD), for electrically connecting and disconnecting the power supplyand the first field effect transistor; a third field effect transistor(70) connected in series with a current output side of the first fieldeffect transistor and having a gate thereof applied with a constantvoltage (VGC2) different from the constant voltage which is applied tothe gate of the first field effect transistor; a fourth field effecttransistor (60) forming a channel different from that of the secondfield effect transistor, connected between a current output side of thethird field effect transistor and a second terminal (a terminal to whichthe ground is connected), and having a gate thereof commonly connectedto an input terminal (IN) together with a gate of the second fieldeffect transistor; and a first output terminal (OUT) connected betweenthe current output side of the third field effect transistor and thefourth field effect transistor through no switching element.

In the present invention as recited in claim 7, as conceptually shown inFIG. 8, the above object is achieved by the provision of a constantcurrent output driver comprising: a first field effect transistor (50)connected to a power supply (VDD), for outputting a constant currentwith the application of a constant voltage (VGC) to a gate thereof; asecond field effect transistor (40) connected in series with a currentoutput side of the first field effect transistor, for conductingswitching operation; a third field effect transistor (70) connected inseries with a current output side of the second field effect transistorand having a gate thereof applied with a constant voltage (VGC2)different from the constant voltage which is applied to the gate of thefirst field effect transistor; a fourth field effect transistor (60)forming a channel different from that of the second field effecttransistor, connected between a current output side of the third fieldeffect transistor and a second terminal, and having a gate thereofcommonly connected to an input terminal (IN) together with a gate of thesecond field effect transistor; and a first output terminal (OUT)connected between the current output side of the third field effecttransistor and the fourth field effect transistor through no switchingelement.

In the present invention as recited in claim 8, as conceptually shown inFIG. 9, the above object is achieved by the provision of a constantcurrent output driver comprising: a first field effect transistor (50)connected to a power supply (VDD), for outputting a constant currentwith the application of a constant voltage (VGC) to a gate thereof; asecond field effect transistor (70) connected in series with a currentoutput side of the first field effect transistor and having a gatethereof applied with a constant voltage (VGC2) different from theconstant voltage which is applied to the gate of the first field effecttransistor; a third field effect transistor (40) connected in serieswith a current output side of the second field effect transistor forconducting switching operation; a fourth field effect transistor (60)forming a channel different from that of the third field effecttransistor, connected between a current output side of the third fieldeffect transistor and a second terminal, and having a gate thereofcommonly connected to an input terminal (IN) together with a gate of thesecond field effect transistor; and a first output terminal (OUT)connected between the current output side of the third field effecttransistor and the fourth field effect transistor through no switchingelement.

In the present invention as recited in claim 9, the above object isachieved by the provision of a constant current output drivercomprising: an output terminal (OUT); a first field effect transistor(50) connected between the output terminal and a power supply (VDD), foroutputting a constant current with the application of a constant voltageto a gate thereof; switching means (40) connected between the firstfield effect transistor and the output terminal or the power supply, forelectrically connecting and disconnecting the first field effecttransistor and the output terminal or the power supply; and a constantvoltage applying circuit (31) having a temperature characteristic whichchanges in the same manner as the temperature characteristic of thefirst field effect transistor, for applying a constant voltage to thefirst field effect transistor at a constant temperature.

In the present invention as recited in claim 10, the above object isachieved by the provision of a constant current output driver in theinvention of claim 9, the constant voltage applying circuit comprises: avoltage dividing means (R), a second field effect transistor (51)connected in serial between the resistor means and the power supply andhaving a gate thereof connected in a saturated state, wherein the gateof the second field effect transistor is connected to the gate of thefirst field effect transistor.

In the present invention as recited in claim 11, the above object isachieved by the provision of a constant current output driver in theinvention of claim 10 wherein the first switching means comprises athird field effect transistor (40) having a gate which inputs aswitching signal; and

wherein there is further provided a fourth field effect transistor (41)which has a gate connected to the ground and is connected to a powersupply side or its opposite side of the second field effect transistorin association with a connection position of the first switching means.

In the present invention as recited in claim 12, the above object isachieved by the provision of a constant current output driver in theinvention of claim 10 wherein the first field effect transistor and thesecond field effect transistor are formed of the same standard elements.

In the present invention as recited in claim 13, the above object isachieved by the provision of a constant current output driver in theinvention of any one of claims 9 to 12 wherein the resistor meanscomprises a ladder resistor, a variable resistor, a terminal to which aresistor is externally attached, or a resistor and a terminal to whichanother resistor is externally attached in parallel to the terminal.

In the present invention as recited in claim 14, the above object isachieved by the provision of a constant current output driver in theinvention of any one of claims 9 to 13 wherein a gate of the secondfield effect transistor is connected to an input of a voltage followercircuit (71), and an output of the voltage follower circuit is connectedto a gate of the first field effect transistor.

In the present invention as recited in claim 15, the above fifth objectis achieved by the provision of a constant current output driver whereinthere are formed, in one integrated circuit, a plurality of outputterminals; field effect transistors the number of which is equal to thatof the output terminals, which are connected between the outputterminals and a power supply and which output a constant current withthe application of a given voltage to gates thereof; switching means forelectrically connecting and disconnecting the respective field effecttransistors and the respective output terminals or the. power supply,independently; a first constant current control section that generates afirst voltage; a second constant current control section that generatesa second voltage; a third constant current control section thatgenerates a third voltage; a first wiring that connects an output of thefirst constant current control section to every three gates of theplurality of field effect transistors; a second wiring that connects anoutput of the second constant current control section to the gates ofthe respective field effect transistors adjacent to the respective fieldeffect transistors to which the first wiring is connected; and a thirdwiring that connects an output of the third constant current controlsection to the gates of the respective field effect transistors furtheradjacent to the respective field effect transistors to which the secondwiring is connected.

As described above, according to the present invention, for example, inthe case where the constant current output driver is applied to anorganic EL panel for color display, three kinds of field effecttransistors that output different constant current values and an outputterminal are disposed in correspondence with the arrangement order ofthree kinds of light emitting elements (the respective light emittingelements of R, G and B) which are sequentially connected to therespective anode terminals A1 to A2 arranged in a line. Accordingly, itis unnecessary to provide multi-layer wirings, and the wiring work issimplified. Also, since the multi-layer wirings is unnecessary, it ispossible to use the constant current output driver for a display unitsuch as an organic EL for color display mounted on a COG.

Also, in the present invention as recited in claim 15, the number of theoutput terminals and the number of the field effect transistors are 192,respectively. In this way, 192 (a common multitude of 3×8) pieces eachof the output terminals and the field effect transistors are arranged.As a result, it is possible to make a chip size (for example, 20 mm)suitable for mounting, and the mounting cost can be reduced.

In the present invention as recited in claim 15, there are provided, inthe claim 15, a first wiring terminal to which the first wiring isconnected, a second wiring terminal to which the second wiring isconnected, and a third wiring terminal to which the third wiring isconnected. Since the respective first to third wiring terminals areconnected in this way, it is possible to monitor the voltage outputtedfrom the first to third constant voltage circuits.

In the present invention as recited in claim 18, there are provided twoof the first constant current control sections, two of the secondconstant current control sections and two of the third constant currentcontrol sections, respectively; wherein the first wiring includes afirst voltage wiring that connects both the outputs of two firstconstant current control sections to each other, and a first gate wiringthat connects the first voltage wiring and the respective gates; whereinthe second wiring includes a second voltage wiring that connects boththe outputs of two second constant current control sections to eachother, and a second gate wiring that connects the second voltage wiringand the respective gates; and wherein the third wiring includes a thirdvoltage wiring that connects both the outputs of two third constantcurrent control sections to each other, and a third gate wiring thatconnects the third voltage wiring and the respective gates.

Since there are provided two first constant current control section, twosecond constant current control section and two third constant currentcontrol section as described above, it is possible to adjust theinclination of a change in the voltage applied to the respective fieldeffect transistors.

Also, in the present invention, a resistor is disposed on a voltagewiring between at least one pair of gate wirings. In this case, thevoltage wiring can be formed of a polysilicon resistor.

Also, in the present invention as recited in claim 21, there are formed,in one integrated circuit, a plurality of output terminals; field effecttransistors the number of which is equal to that of the outputterminals, which are connected between the output terminals and a powersupply and which output a constant current with the application of agiven voltage to gates thereof; switching means for electricallyconnecting and disconnecting the respective field effect transistors andthe respective output terminals or the power supply, independently;first, second and third voltage input terminals to which a voltage isapplied; first, second and third voltage output terminals from which thevoltage is outputted; a first voltage wiring that connects the firstvoltage input terminal and the first voltage output terminal; a secondvoltage wiring that connects the second voltage input terminal and thesecond voltage output terminal; a third voltage wiring that connects thethird voltage input terminal and the third voltage output terminal; afirst gate wiring that connects the first voltage wiring to every threegates of the plurality of field effect transistors; a second gate wiringthat connects the second voltage wiring to the gates of the respectivefield effect transistors adjacent to the respective field effecttransistors to which the first wiring is connected; and a third gatewiring that connects the third voltage wiring to the gates of therespective field effect transistors further adjacent to the respectivefield effect transistors to which the second wiring is connected.

As the piezoelectric input terminal to which a voltage is applied isprovided as described above, the first voltage, the second voltage andthe third voltage applied to the gates of the field effect transistorscan be applied from the exterior of the constant current output driver.In addition, since the voltage output terminals from which the voltageis outputted are provided, it is possible to sequentially connect aplurality of constant current output drivers. Also, the first voltage,the second voltage and the third voltage can be applied from the voltageoutput terminal, and since there is provided a difference between theapplied voltage from the voltage input terminal and the applied voltagefrom the voltage output terminal, it is possible to adjust theinclination of a change in the voltage applied to the respective fieldeffect transistors.

In the present invention, there may be used the voltage supply device ofthe constant current output driver in which there is formed, in oneintegrated circuit, a first constant current control section thatgenerates the first voltage, a second constant current control sectionthat generates the second voltage, a third constant current controlsection that generates the third voltage, a first terminal to which theoutput of the first constant current control section is connected, asecond terminal to which the output of the second constant currentcontrol section is connected, and a third terminal to which the outputof the third constant current control section is connected, and thefirst, the second and the third terminals are connected to the first,the second and the third voltage input terminals to apply a voltage.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a conceptual diagram corresponding to claim 1 of the presentinvention,

FIG. 2 is a conceptual diagram corresponding to claim 2 of the presentinvention,

FIG. 3 is a structural diagram showing an example corresponding to claim3 of the present invention,

FIG. 4 is a structural diagram showing an example corresponding to claim4 of the present invention,

FIG. 5 is a structural diagram showing an example corresponding to claim5 of the present invention and a structural diagram of a firstembodiment mode corresponding to the respective inventions,

FIG. 6 is an explanatory diagram showing the simulation result of aconstant current output driver having the structure of FIG. 5,

FIG. 7 is a structural diagram showing an example corresponding to claim6 of the present invention,

FIG. 8 is a structural diagram showing an example corresponding to claim7 of the present invention,

FIG. 9 is a structural diagram showing an example corresponding to claim8 of the present invention,

FIG. 10 is a structural diagram of a second embodiment mode of thepresent invention,

FIG. 11 is an explanatory diagram showing the simulation result of aconstant current output driver having the structure of FIG. 10,

FIG. 12 is a circuit structural diagram of a constant current outputdriver in a third embodiment mode of the present invention,

FIG. 13 is an explanatory diagram showing an influence of thetemperature change on a constant current FET and a constant currentcontrol FET in the above third embodiment mode,

FIG. 14 is a circuit structural diagram of a constant current outputdriver in a fourth embodiment mode of the present invention,

FIG. 15 is a circuit structural diagram of a constant current outputdriver in a fifth embodiment mode of the present invention,

FIG. 16 is a circuit structural diagram of a constant current outputdriver in a sixth embodiment mode of the present invention,

FIGS. 17 A-C are an explanatory diagram of a case in which a pluralityof constant current output drivers are disposed in the sixth embodimentmode of the present invention,

FIGS. 18 are a circuit structural diagram (a) of a constant currentoutput driver in a seventh embodiment mode of the present invention, andan explanatory diagram (b) of voltage adjustment,

FIGS. 19 are a circuit structural diagram (a) of a constant currentoutput section in an eighth embodiment mode of the present invention,and an explanatory diagram (b) of voltage adjustment,

FIGS. 20 are a circuit structural diagram of a constant current outputdevice (a) and a constant voltage generating device (b) in a ninthembodiment mode of the present invention.

FIG. 21 is an explanatory diagram showing the use condition in the ninthembodiment mode of the present invention,

FIG. 22 shows the structure of a conventional display unit using anorganic EL,

FIG. 23 is a structural diagram proposed in a case where theconventional constant current output driver is formed of an enhancementMOSFET,

FIG. 24 is an explanatory diagram showing the simulation result of aconstant current output driver having the structure of FIG. 22, and

FIG. 25 shows the structure of the conventional display unit in whichthe conventional constant current output drive is formed of anenhancement MOSFET to conduct color display on the organic EL panel.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, a description will be given in detail of a preferred firstembodiment mode in a constant current output driver

according to the present invention with reference to FIGS. 2, 5 and 6.

FIG. 5 shows the circuit structure of a constant current output driver.

The constant current output driver according to this embodiment mode canbe applied to a driver for an LED panel and other devices that requirethe constant current drive, and in particular, is effective to a case inwhich an organic EL panel shown in FIG. 22 with a problem of adifference in the wiring resistance within the panel is employed.

As shown in FIG. 5, the constant current output driver according to thisembodiment mode includes a constant current FET 50 formed of a p-channelMOSFET, a switch FET 40 formed of a p-channel MOSFET and a switch FET 60formed of an n-channel MOSFET. The constant current FET 50 and theswitch FETs 40 and 60 are formed of the enhancement MOSFET,respectively.

A source S of the switch FET 40 is connected to a power supply VDD (30 Vin this embodiment mode), a drain D of the switch FET 40 and a source Sof the constant current FET 50 are connected to each other, and both ofa drain D of the constant current FET 50 and a drain D of the switch FET60 are connected to an output terminal OUT. A source S of the switch FET60 and a substrate B are connected to the ground. Because a constantvoltage (VGC) is applied to a gate G of the constant current FET 50, theFET 50 outputs a constant current in a saturation operating range.

Both of a gate G of the switch FET 40 and a gate G of the switch FET 60are connected to an input terminal IN. With this structure, the switchFET 60 conducts the off/on operation in association with the on/offoperation of the switch FET 40. A constant gate voltage VGC is alwaysapplied to the gate G of the constant current FET 50 in order to makethe constant current FET 50 function as the constant current element.

A substrate B of the. switch FET 60 is connected to the ground commonlytogether with the source S.

Also, the substrate B of the constant current FET 50 and the substrate Bof the switch FET 40 are connected to the power supply VDD together. Asa result, the substrate potential of both the substrates B of theconstant current FET 50 and the switch FET 40 are common to each otherand also common to the source potential of the constant current FET 40.

The drive circuit 3 is formed of m constant current output drivers thusstructured, and the organic EL display unit is structured by connectingthe respective constant current output drives to the anode lines A1 toAm.

In the above constant current output driver, in a state where an H(high) level signal is supplied from the input terminal IN, thep-channel switch FET 40 comes to an off-state because no channel isformed, and the constant current FET 50 and the power supply VDD areelectrically separated from each other. Therefore, no current flows inthe output terminal OUT. On the other hand, in the case where the inputterminal IN is of the H level, because the n-channel switch FET 60 isformed with a channel and comes to an on-state, the output terminal OUTis connected to the ground through the switch FET 60.

Then, when the switching signal is changed over and an L (low) levelsignal is supplied from the input terminal IN, the channel of the switchFET 60 disappears and is electrically separated from the output terminalOUT. Also, a channel is formed in the switch FET 40, and the powersupply VDD and the constant current FET 70 are connected to each other.As a result, a constant current is supplied to the output terminal OUTfrom the power supply VDD through the constant current FET 70.

FIG. 6 shows the simulation result of an output current in the constantcurrent output driver in accordance with this embodiment mode. In thefigure, the axis of abscissa is a time t whereas the axis of ordinate isa current value I of the output terminal OUT.

As shown in FIG. 6, according to the constant current output driver ofthis embodiment mode, over-shoot does not occur in a moment when theswitch FET 40 and the switch FET 60 turn on and off as indicated byarrows A and B.

The current in a minus direction indicated by an arrow C shown in FIG. 6is obtained by discharging the charges stored in the capacity componentof an organic EL connected to the output terminal OUT to the ground asin the arrow C of FIG. 24 and is not over-shoot (the same is applied tothe simulation result shown in FIG. 11 which will be described later).

As shown in FIG. 6, according to the constant current output driver withthe structure shown in FIG. 5, the occurrence of over-shoot is preventedfor the following reasons.

In the constant current output driver according to this embodiment mode,no switching element exists between the constant current FET 50 and theoutput terminal OUT, and the switch FET 40 is connected to the powersupply VDD side rather than the constant current element 50. For thatreason, even if over-shoot occurs in the output current of the switchFET 40 due to the on/off operation of the switch FET 40, since theconstant current FET 50 is disposed between the output terminal OUT andthe switch FET 40, constant current with no over-shoot is outputted tothe output terminal OUT. In this example, the over-shoot is directed toa current that flows through the capacitor of the gate insulating filmof the switch FET 40.

Also, in the constant current output driver according to this embodimentmode, since the substrate B of the constant current FET 50 is connectedto the power supply VDD, even if the switch FET 40 turns on/off, thepotential of the substrate B of the constant current FET 50 does notfluctuate and is kept constant. For that reason, the constant currentFET 50 can stably output the constant current from the output terminalOUT without being adversely affected by the operation of the switch FET40.

In addition, in the constant current output driver according to thisembodiment mode, since the substrate B of the constant current FET 50and the substrate B of the switch FET 40 are common to each other, if awell is commonly used, the chip size can be reduced.

However, in the constant current output driver with the structure shownin FIG. 5, in order to reduce the output terminal OUT voltage dependencychange of the constant current value, it is necessary to increase thegate length of the constant current FET 50 with such a problem that theIC chip size increases. Also, because the constant current FET 50 isdirectly connected to the output terminal OUT which is large in voltagefluctuation due to switching, there arises such a problem that the gatevoltage VGC of the constant current FET fluctuates with receiving aninfluence of switching, and the constant current value fluctuates.

FIG. 2 is a conceptual diagram showing the MOSFET shown in FIG. 5 beingrepresented by a constant current element 100, a switch 101 and a switch103. As shown in FIG. 2, the first embodiment mode can be realized byanother element instead of the MOSFET. However, for the reasons such asthe low power consumption, downsizing is easy and the controllability ofthe constant current which will be described below is facilitated, thestructure shown in FIG. 5 is more desirable.

FIG. 3 is a structural diagram showing a structure in which the switchFET 60 and the ground are removed from FIG. 5. Even in the structureshown in FIG. 3, it is possible to provide the constant current outputwithout over-shoot as in the case of FIG. 5. In the case of driving theorganic EL panel, since it is necessary that the potential of the outputterminal OUT drops to the ground, the structure shown in FIG. 5 isdesirable.

FIG. 1 is a conceptual diagram showing the MOSFET shown in FIG. 3 beingrepresented by the constant current element 100 and the switch 101. Forthe same reasons as those in the case of FIG. 2, the structure of FIG. 3is more desirable than that of FIG. 1.

FIG. 4 shows the structure in which an FET 70 is connected in seriesbetween the constant current FET 50 shown in FIG. 3 and the outputterminal OUT. A constant voltage (VGC) is applied to the gate of theconstant current FET 50, and a constant voltage (VGC2) different fromthe gate voltage of the constant current FET 50 is applied to the gateof the FET 70. In this example, the VGC 2 is so set as to provide adifference from VGC to the degree that the FET 70 conducts saturationoperation.

With the above-described structure shown in FIG. 4,the FET 70 issubjected to cascade-connection and even in the case where a voltagebetween the source S of the FET 50 and the drain D of the FET 70 largelychanges, a voltage between the source S and the drain D of the FET 50hardly changes. Accordingly, the output terminal OUT voltage dependencychange of the output constant current value becomes very small ascompared with the structure shown in FIG. 3.

In the structure shown in FIG. 4, it is desirable that the channelwidth/channel length of the constant current FET 50 are made identicalwith the channel width/channel length of the FET 70. In the case wherethe above values are made identical, if the VGC and the VGC2 are set sothat the ratio of VGC-VDD-(threshold voltage of FET 50) andVGC2-VDD-(threshold voltage of FET 70) becomes 1:2, the FET 70 alwaysconducts saturation operation, and a change in the output constantcurrent value of the constant current FET 50 depending on the outputterminal OUT voltage becomes very small. Also, the output terminal OUTvoltage range which can output the constant current becomes maximum. Inaddition, it becomes easy to set the voltage of VGC and VGC2.

FIG. 7 shows the structure in which the switch FET 70 is connected inseries between the constant current FET 50 shown in FIG. 5 and theoutput terminal OUT. A constant voltage (VGC) is applied to the gate ofthe constant current FET 50, and a constant voltage (VGC2) differentfrom the gate voltage of the constant current FET 50 is applied to thegate of the FET 70. In this example, the VGC 2 is so set as to provide adifference from VGC to the degree that the FET 70 conducts saturationoperation.

The structure shown in FIG. 7 is suitable for driving of the organic ELpanel since it has a function that outputs the ground to the outputterminal OUT. Also, if the channel width/channel length of the constantcurrent FET 50 are made identical with the channel width/channel lengthof the FET 70, as in the above case of FIG. 4, a change of the outputconstant current value depending on the output terminal OUT voltagebecomes very small and the output terminal OUT voltage range which canoutput the constant current becomes maximum. Therefore, the structure ofFIG. 7 is very suitable for driving of the organic EL panel in which adifference in the wiring resistance within the panel is largelyeffected.

Also, in the structure of FIG. 7, no over-shoot of the output constantcurrent value occurs as in the case of FIG. 5. In addition, because theconstant current FET 50 is connected to the output terminal OUT large involtage fluctuation due to switching through the FET 70, the gatevoltage VGC of the constant current FET is hardly affected by switching.

The structure of FIG. 8 is stated below. The power supply VDD isconnected with the source S of the constant current FET 50, the drain Dof the constant current FET 50 is connected with the source of theswitch FET 40, the drain D of the constant current FET 50 is connectedwith the source S of the FET 70, and both of the drain D of the FET 70and the drain D of the switch FET 60 are connected to the outputterminal OUT. The source S of the switch FET 60 and the substrate B areconnected to the ground. Other structures are the same as those in FIG.7.

With the above-described structure, because the source S of the constantcurrent FET 50 is directly connected to the power supply VDD, adifference in voltage between VGC and VDD becomes high in accuracy, andthe accuracy in the output constant current value also becomes high.Also, since the constant current FET 50 and the FET 70 are connected inseries, a change of the output constant current value depending on theoutput terminal OUT voltage becomes very small as in the case of FIG. 7.In addition, because the FET 70 acts in the same manner as that of theconstant current FET 50, over-shoot of the output current is larger thanthat in FIG. 7 but prevented to some degree. Also, the gate voltage VGCof the constant current FET 50 is hardly affected by switching as inFIG. 7.

However, since the switch FET 40 exists between the constant current FET50 and the FET 70, it is necessary to increase a difference in voltagebetween VGC and VGC2 more than the above-described case of FIG. 7, andtherefore there arises such a defect that the output terminal OUTvoltage range that can output the constant current is narrower than thatof FIG. 7 as much.

The structure of FIG. 9 is stated below. The power supply VDD isconnected with the source S of the constant current FET 50, the drain Dof the constant current FET 50 is connected with the source S of the FET70, the drain D of the FET 70 is connected with the source of the switchFET 40. Also, both of the drain D of the switch FET 40 and the drain Dof the switch FET 60 are connected to the output terminal OUT. Thesource S of the switch FET 60 and the substrate B are connected to theground. Other structures are the same as those in FIG. 7.

With the above-described structure, the output constant current valuebecomes high in accuracy as in the case of FIG. 8. Also, since theconstant current FET 50 and the FET 70 are connected in series, a changeof the output constant current value depending on the output terminalOUT voltage becomes very small as in the case of FIG. 7. In addition,the FET 50 is not directly connected to the output terminal OUT and alsois not directly connected to both of the FET 40 and the FET 60 whichconduct switching. For that reason, it is difficult that the VGC voltageis affected by switching as compared with the structures of FIGS. 7 and8.

Subsequently, a second embodiment mode of the constant current outputdriver will be described.

FIG. 10 is a diagram showing the circuit structure of a constant currentoutput driver in accordance with the second embodiment mode.

As shown in FIG. 10, the constant current output driver according to thesecond embodiment mode is so modified as to connect the substrates B ofthe respective FETs shown in FIG. 5 to the respective sources S, andother structures are identical with the case of the first embodimentmode shown in FIG. 5.

FIG. 11 shows the simulation result of an output current in the constantcurrent output driver shown in FIG. 10 in accordance with the secondembodiment mode.

As shown in FIG. 11, according to the constant current output driver ofthis embodiment mode, over-shoot occurs as indicated by an arrow A in amoment when the switch FET 40 turns on but is suppressed to ¼ or less ascompared with over-shoot indicated by the arrow A in FIG. 24. Also,over-shoot does not occur as indicated by the arrow in a moment when theswitch FET 40 turns off.

In the structure of FIG. 10, the reason why small over-shoot indicatedby the arrow A in FIG. 23 occurs although the constant current FET 50exists between the switch FET 40 and the output terminal OUT as in thecase of FIG. 7 is that a current flows through the capacity componentbetween the substrate B and drain D of the constant current FET 50. Thatcomponent is directed to minus in the arrow B of FIG. 23.

As described above, the structure of FIG. 11 is inferior to that of FIG.7 in that the over-shoot of the output current slightly occurs. However,in the case where it is necessary to take the potential of the substrateB for each FET without forming a well as in the case where the driver isformed on the SOI substrate, since the wiring from the substrate B ismerely connected to the source close to the substrate B without drawingthe wiring to VDD or the ground far from the substrate B, there is anadvantage in which the chip area can be reduced.

As described above, similarly, in the second embodiment mode, since theswitch FET 40 is disposed between the constant current FET 70 and thepower supply VDD without disposing the switch element between theconstant current FET 50 and the output terminal OUT, the occurrence ofover-shoot can be suppressed.

The above description is given of the constant current output driver inthe first embodiment mode and the second embodiment mode. However, thepresent invention is not limited to those structures, and variousmodifications are enabled in the scope of the invention recited in theclaims. For example, in the embodiment mode, the constant current outputdrive functions as the constant current element by applying the constantvoltage VGC to the gate G of the enhancement p-channel MOSFET. Also, theconstant current output drive may function as the constant currentelement by using the enhancement n-channel MOSFET or by using thedepletion MOSFET.

Subsequently, a third embodiment mode of the present invention will bedescribed in detail with reference to FIGS. 12 and 13.

FIG. 12 shows the circuit structure of a constant current output driver.

As shown in FIG. 12, the constant current output driver according tothis embodiment mode is made up of a constant current output section 30and a constant current control section 31.

In the case where the constant current output section 30 is connected tothe organic EL panel 1 shown in FIG. 22, there exist the constantcurrent output sections 30 of the same number m as m which is the numberof the respective anode lines A1 to Am, or of the number m/n (n is thenumber when a plurality of constant current output drivers are used) asin the drive circuit 3. However, because those constant current outputsections 30 are of the same structure, one constant current outputsection 30 will be shown and described.

One constant current control section 31 exists. Then, the output of oneconstant current control section is inputted in parallel to therespective input sections of a plurality of constant current outputsections 30 (the gates Gs of the constant current FETs 50 which will bedescribed). Also, the constant current control section 31 is sostructured as to have the same temperature characteristics as those ofthe constant current output section 30.

That is, the constant current output driver according to this embodimentmode is made up of one constant current control section 31 and aplurality of constant current output sections 30 connected in parallelwith the constant current control section 31. Note that the aboverelationship is also applied to other embodiment modes which will bedescribed later.

The constant current output section 30 is identical in structure withthat of FIG. 5 which was described in the first embodiment mode.

On the other hand, the constant current control section 31 is designedin such a manner that the output system including elements of from thepower supply VDD to the output section P is formed of the same elementsas those which constitute the output system including elements of fromthe power supply VDD to the output terminal OUT in the constant currentoutput section 30 so that the temperature characteristic of the constantcurrent control section 31 is identical with that of the constantcurrent output section 30.

In other words, the constant current control section 31 includes aconstant current control FET 51 formed of a p-channel MOSFET having thesame characteristic (the same standard) as that of a switch FET 40, anda characteristic adjusting FET 41 formed of a p-channel MOSFET havingthe same characteristic as that of a constant current FET 50. Theconstant current control section 31 also includes a resistor R whichdivides the power supply VDD to adjust a voltage applied to the constantcurrent FET 50, and an operational amplifier 71 connected in voltagefollower. In this example, it is desirable that the gate length, thegate width, VTH and the gate insulating film thickness of the constantcurrent control FET 51 are made coincident with the gate length, thegate width, VTH and the gate insulating film thickness of the constantcurrent FET 50, because the temperature characteristic is equal betweenthe FETs 50 and 51 not depending on a set output current value. In orderto reduce the current consumption of the constant current controlsection 31, the gate width of the constant current control FET is madesmaller than that of the constant current FET 50, and the value of (gatewidth/gate length), VTH and the gate insulating film thickness of theconstant current control FET 51 are made coincident with those of theconstant current FET 50.

The constant current control FET 51. and the characteristic adjustingFETs 41 and 60 are of the enhancement MOSFET, respectively.

The source S of the characteristic adjusting FET 41 is connected to thepower supply VDD and connected with the drain D of the characteristicadjusting FET 41 and the source S of the constant current control FET51.

The gate G of the characteristic adjusting FET 41 is connected to theground. For that reason, the characteristic adjusting FET 41 is alwaysin the on-state, and the temperature characteristic in the output systemof the constant current control section 31 is so adjusted as to have thesame temperature characteristic as that of the output system includingthe characteristic adjusting FET 41 of the constant current outputsection 30.

The gate G of the constant current control FET 51 is connected to thedrain D thereof. In this way, the constant current control FET 51 isstructured to always operate in the saturated region by connecting thegate G in the saturated manner.

The drain D (gate G) of the constant current control FET 51 is connectedto the non-inverse input terminal of the operational amplifier 71 andalso connected to one end of the resistor R for dividing the voltage ofthe power supply VDD.

The operational amplifier 71 is connected to the gate G of the constantcurrent FET 50 through the output section P of the constant currentcontrol section 31. Also, the operational amplifier 71 constitutes avoltage follower circuit by direct connection of the output terminal tothe inverse input terminal. The operational amplifier 71 having voltagefollower connection is used to stabilize the output of the constantcurrent control FET 51.

Another end of the resistor R is connected to the ground.

The resistance value of the resistor R is set so that a desired gatevoltage VGC is applied to the gate G of the constant current FET 50through the operational amplifier 71 and the output section P. The draincurrent I1 of the constant current FET 50 is determined in accordancewith the set gate voltage VGC. The current value of the drain current I1is a given current value necessary for light emission of the organic ELof the organic EL panel 1, and for example, I1=200 {grave over (l)}A isused.

As the resistor R for obtaining a given gate voltage VGC, a resistorhaving a resistance value adjusted in advance can be used, however, avariable resistor may be used or the resistance values of a plurality ofresistors may be adjusted by fuse trimming.

Subsequently, the operation of the constant current output driver thusstructured will be described.

First, a case in which the temperature is of a given value T1 and notchanged will be described.

In this case, the constant current control section 31 applies to thegate G of the constant current FET 50 a given gate voltage VGC which isset without being affected by the temperature since the temperature isconstant.

On the other hand, when the constant gate voltage VGC is applied to thegate G, the constant current FET 50 outputs and stops the drain currentI1 corresponding to the gate voltage VGC in accordance with the on/offoperation of the switch FET 40.

In other words, in a state where an H (high) level signal is suppliedfrom the input terminal IN, the p-channel switch FET 40 comes to anoff-state because no channel is formed, and the constant current FET 50and the power supply VDD are electrically separated from each other.Therefore, no drain current I1 flows in the output terminal OUT. On theother hand, in the case where the input terminal IN is of the H level,because the n-channel switch FET 60 is formed with a channel and comesto an on-state, the output terminal OUT is connected to the groundthrough the switch FET 60.

Then, when the switching signal is changed over and an L (low) levelsignal is supplied from the input terminal IN, the channel of the switchFET 60 disappears and is electrically separated from the output terminalOUT. Also, the switch FET 40 is formed with a channel and comes to theon-state, and the power supply VDD and the constant current FET 50 areconnected to each other. As a result, a constant drain current I1 issupplied to the output terminal OUT from the power supply VDD. throughthe constant current FET 50.

Subsequently, the operation of the constant current output driver in acase where the temperature changes from T1 to T2 will be described.

FIG. 13 shows the influence of a change in temperature in the constantcurrent FET 50 and the constant current control FET 51.

In FIG. 13, a curve T1 represents the gate voltage to the drain currentcharacteristic curves T1 and T2 of the constant current FET 50 and theconstant current control FET 51 at a temperature T1. Thosecharacteristic curves T1 and T2 are represented by nearly curves of thesecond order.

As shown in FIG. 13, a relationship between the gate voltage and thedrain current of the constant current FET 50 has a characteristic thatchanges the curve from T1 to T2 depending on the temperature T. For thatreason, if VGC applied to the gate G of the constant current FET 50 isalways constant at the temperatures T1 and T2, the drain current Idwhich was I1 at the temperature T largely changes to I3 at thetemperature T2. Because the drain current Id changes by nearly square ofthe gate voltage as shown in the curve T1, the output current suppliedto the organic EL panel 1 from the output OUT terminal largely changesdepending on the temperature with the result that a constant luminanceis not obtained.

On the contrary, the constant current control FET 51 of the constantcurrent control section 31 according to this embodiment mode isconnected in series to the resistor R and the gate G is connected in thesaturated manner. For that reason, the drain current that flows in theconstant current control FET 51 is determined by the intersection of thecharacteristic curves T1 and T2 of the constant current control FET 51with a straight line R due to the resistor R.

Accordingly, the drain current of the constant current control FET 51only changes from the drain current I1 determined by the intersection ofthe characteristic curve T1 with the straight line R to the draincurrent I2 determined by the intersection of the characteristic curve T2with the straight line R even if the temperature changes from T1 to T2.The drain current of the constant current control FET 51 is slightlyaffected by the temperature but its influence can be suppressed to asmall degree.

In other words, in the case where the temperature goes down from T1 toT2, the gate voltage drop from VGC1 to VGC2 so that the voltage VGSbetween the gate G and the power supply VDD (which can approximate tothe voltage between the gate and the source S) increases from VGS1 toVGS2. For that reason, even if the temperature goes down to T2, thedrain current I2 larger than the current I3 in the case where thevoltage VGS is kept to VGS1 flows. Accordingly, the amount of a changefrom the drain current I1 at the time of the temperature T1 can besuppressed to the small value.

In this embodiment mode, as shown in FIG. 12, the output system (fromthe power supply VDD to the output section P) of the constant currentcontrol section 31 and the output system (from the power supply VDD tothe output OUT) of the constant current output section 30 are identicalin structure with each other. In addition, since the gate G of theconstant current control FET 51 is connected to the gate G of theconstant current FET 50 through the operational amplifier 71 having thevoltage follower connection, both of the gate voltages of the constantcurrent control FET 51 and the constant current FET 50 are identicalwith each other.

Accordingly, the constant current FET 50 operates with respect to thetemperature change as in the constant current control FET 51. In otherwords, in the case where the temperature changes from T1 to T2, thedrain current of the constant current FET 50 largely changes from I1 toI3 if the gate voltage is constant. However, the gate voltage alsochanges from VGC1 to VGC2 as the temperature changes, the drain currentof the constant current FET 50 is suppressed to the small change of fromI1 to I2.

As described above, according to this embodiment mode, the output systemin the constant current control section 31 is made identical instructure with the output system in the constant current output section30 at the time of the on-state, and the gate G of the constant currentcontrol FET 51 corresponding to the constant current FET 50 is connectedin the saturated manner and connected to the gate G of the constantcurrent FET 50. Therefore, a change in the output current (draincurrent) of the constant current FET 50 which constitutes the constantcurrent output section 30 depending on the temperature can be suppressedto the small value.

Also, according to this embodiment mode, the output system in theconstant current control section 31 is made identical in structure withthe output system in the constant current output section 30 at the timeof the on-state.

In other words, the constant current control FET 51 having the samecharacteristic as that of the constant current FET 50 is employed. Inaddition, taking the temperature characteristic of the output currentdue to the switch FET 40 into consideration, adjustment is made so thatthe switch FET 40 has the same characteristic as that in the on-state bythe following manner. That is, the characteristic adjusting FET 41having the same characteristic as that of the switch FET 40 is connectedin the same manner as that of switch FET 40, and the gate G of thecharacteristic adjusting FET 41 is connected to the ground and alwaysbecomes in the on-state. As a result, the drain current of the constantcurrent FET 50 and the drain current of the constant current control FET51 can be made identical with each other.

For that reason, in the case where the constant current value suppliedto the organic EL panel 1 from the plural constant current outputsections 30, respectively, is adjusted to a given current value, forexample, 200 {grave over (l)}A, if one resistance value of the resistorR in the constant current control section 31 is adjusted to set thedrain current of the constant current control FET 51 to a desired value(200 {grave over (l)}A, etc.), it is possible to adjust the draincurrent of the constant current FET 50 to a desired value.

In other words, since there is no necessity that an adjustment elementor the like is disposed on each of the constant current output sections30, or the drain current of the constant current FET 50 is adjusted foreach of the constant current output sections 30, the element isdownsized, and the output current adjustment is facilitated.

Subsequently, a fourth embodiment mode will be described with referenceto FIG. 14.

FIG. 14 shows the structure of a constant current output driver in thefourth embodiment mode. The constant current output driver according tothis embodiment mode is made up of one constant current control section31 and a plurality of constant current output sections 30 connected inparallel with the constant current control section 31, as in the thirdembodiment mode.

In FIG. 14 and FIG. 15 which will be described later, the substrates Bof the respective FETs are connected to the sources S in the same manneras that of the second embodiment mode. As described in the first andsecond embodiment modes, in order to reduce the over-shoot of the outputconstant current, it is desirable that the potential of the substrates Bof all the FETs in FIGS. 14 and 15 is connected to VDD or VDD. However,for facilitation of understanding the figures, in this example, thesubstrate B of the FET is connected to the source S.

As shown in FIG. 14, in the constant current output section 30 accordingto the fourth embodiment mode, the substrate B of the constant currentFET 50 is connected to not the power supply VDD but the drain D of theswitch FET 40, and other structures are identical with those in thethird embodiment mode.

Also, the constant current control section 31 is different from that inthe third embodiment mode in that the substrate B of the constantcurrent control FET 51 is connected to not the power supply VDD but thedrain D of the characteristic adjusting FET 41, and in that the gate Gof the constant current control FET 51 saturation-connected to the drainD is directly connected to the gate G of the constant current FET 50 notthrough the operational amplifier 71. Also, in the constant currentcontrol section 31, both ends of the resistor R are connected withterminals 81 a and 81 b for externally connecting a resistor r foradjustment of the resistance value in parallel with the resistor R.Other structures are identical with those in the first embodiment mode.

Similarly, in this embodiment mode, the output system (from the powersupply VDD to the output section P) of the constant current controlsection 31 and the output system (from the power supply VDD to theoutput OUT) of the constant current output section 30 are identical instructure with each other. The influence due to the temperature changeon the output current in the constant current output section 30 can besuppressed to a small degree.

Also, in this embodiment mode, in the case where the output current ofthe constant current output section 30 (the drain current of theconstant current FET 50) is set to a desired value, if the resistor R isadjusted so that the drain current of the constant current control FET51 in the constant current control section 31 is set to the same desiredvalue, adjustment can be readily made.

Also, since the gate G of the constant current control FET 51 isdirectly connected to the gate G of the constant current FET 50 notthrough the operational amplifier 71, it is possible to reduce the powerconsumption. Accordingly, similarly in the first embodiment mode, if theoperational amplifier 71 is omitted, and the gate G of the constantcurrent control FET 51 is directly connected to the gate G of theconstant current FET 50, the power consumption can be reduced.

Also, according to the fourth embodiment mode, since the terminals 81 aand 81 b for connecting the external resistor r for adjustment of theresistance value in parallel with the resistor R are provided, the fineadjustment can be conducted by the external resistor r with the resistorR as the fixed value. In this manner, since the terminals 81 a and 81 bfor externally connecting the resistor are disposed, the constantcurrent output driver can be adjusted from the external. Note that theconstant current control section 31 may provide only the externalterminals 81 a and 81 b without provision of the resistor R. In thiscase, the external resistor r is connected between the terminals 81 aand 81 b after the constant current output driver has been manufacturedso that the output current (the drain current of the constant currentFET 50) becomes a given value (for example, 200 micro A).

The structure of providing the terminals 81 a and 81 b for connectingthe resistor r for adjustment of the resistance value (including a casein which only the terminals 81 a and 81 b are connected without theresistor R) in the above fourth embodiment mode can be applied to thethird embodiment mode, likewise, and also can be applied to otherrespective embodiment modes which will be described later.

Subsequently, a fifth embodiment mode will be described.

FIG. 15 shows the structure of a constant current output driver in thefifth embodiment mode. The constant current output driver according tothis embodiment mode is made up of one constant current control section31 and a plurality of constant current output sections 30 connected inparallel with the constant current control section 31, as in the firstembodiment mode.

In the fifth embodiment mode, the constant current output driverdescribed with reference to FIG. 23 is used as the constant currentoutput section 30, and the constant current control section 31 isstructured in the same arrangement as the constant current FET 50, theswitch FET 40 and the switch FET 60 in the constant current outputsection 30.

In the constant current control section 31 of this embodiment mode, thegate G of the constant current control FET 51 is saturation-connected tothe drain D of the constant current control FET 51.

Similarly, in the fifth embodiment mode, since the output system of theconstant current control section 31 and the output system of theconstant current output section 30 are identical in structure with eachother, a fluctuation of the output current in the constant currentoutput section 30 due to the temperature change can be suppressed to asmall degree.

Also, in the case where the output current of the constant currentoutput section 30 (the drain current of the constant current FET 50) isset to a desired value, if the resistor R is adjusted so that the draincurrent of the constant current control FET 51 in the constant currentcontrol section 31 is set to the same desired value, adjustment can bereadily made.

As described in the above third to fifth embodiment modes, as thestructure of the constant current output section 30, the connection ofthe constant current FET 50 and the switch FET 40 can be made withvarious connections, and even in any one of the structures describedabove or other structures, with the connection of the constant currentcontrol section 31 having the temperature characteristic of the sametendency (including the same case) as described in the third to fifthembodiment modes, the amount of a change in the drain current of theconstant current FET 50 due to the temperature change can be suppressedto a small value.

However, in the constant current output section 30 in the constantcurrent output driver, taking over-shoot in the on-state due to theon/off of the input IN, etc., into consideration, it is most desirablethat the arrangement is selected from the constant current outputsection 30 in the first embodiment mode, and the constant currentcontrol section 31 having the same FET arrangement is selected.

Hereinafter, the preferred sixth embodiment mode in the constant currentoutput driver according to the present invention will be described indetail with reference to FIG. 16.

As shown in FIG. 16, the constant current output sections 301 to 30sthat output a constant current in accordance with the value of theapplied gate voltage VGC are connected to the output terminals O1 to Osarranged in a line. The gates of those constant current output sections301 to 30s are connected to three constant current control sections 31R,31G and 31B which generate the gate voltages for R, G and B in thestated order. In other words, the respective current control sections31R, 31G and 31B are connected to every three constant current outputsections 301 to 30s by the voltage wirings 321R, 321G and 321B and thegate wirings 322R, 322G and 322B, respectively. With this structure, theoutput terminals O1 to Os output the respective constant currents for R,G and B in the arrangement order.

Consequently, it is possible that the wirings from the output terminalsO1 to Os of the constant current output driver with respect to the colororganic EL panel 1 having the anode terminals A1 to A2 arranged in aline are formed of a single layer.

The constant current output driver 3 in this embodiment mode can be usednot only as the drive circuit 3 in the display unit using the organic ELpanel 1 for color display which was described with reference to FIGS. 22and 25, but also as a driver of the LED panel or a device that requiresthe constant current drive.

FIG. 16 shows the circuit structure of the constant current outputdriver 3.

As shown in FIG. 16, the constant current output driver 3 includes soutput terminals O1 to Os, s constant current output sections 301 to30s, three wiring terminals TR, TG and TB, and three constant currentcontrol sections 31R, 31G and 31B.

When the common contents will be described without specificallydesignating the output terminals O1 to Os, the constant current outputsections 301 to 30s, the wiring terminals TR, TG and TB, and theconstant current control sections 31R, 31G and 31B, they will bedescribed as the output terminal O, the wiring terminal T, the constantcurrent output section 30 and the constant current control section 31,respectively. The same is applied to other elements.

The output terminals O1 to Os are arranged in a line in the ordercorresponding to the anode line terminals A1 to As of a display unit towhich the constant current output driver 3 is applied, for example, thecolor organic EL panel 1 shown in FIG. 16. In this embodiment mode, theoutput terminals O1 to Os are arranged in a line, but if thesingle-layer wiring with the color organic EL panel 1 is enabled, theoutput terminals O1 to Os may be arranged in zigzags so as to bearranged in plural lines.

Also, the number s of the output terminals O1 to Os is made coincidentwith the number s of the anode line terminals A of the color organic ELpanel 1, but may be set to 1/w (w is a positive number) of the number ofthe anode line terminals A to drive the color organic EL panel 1 byusing the w constant current output drivers 3.

In addition, it is preferable that the number s is the multiple of thenumber 3 of the three primary colors R, G and B necessary for colordisplay and also the multiple of the number 8 that constitutes one byte.Also, s=192 is applied in this embodiment mode from the viewpoint of theactual resolution of the display panel and this number is mostdesirable.

The s constant current output sections 30 are disposed in correspondencewith the number s of the output terminals O. The constant current outputsections 30 are formed of field effect transistors (FETs). All of theconstant current output sections 30 are identical in structure with eachother and designed so that a constant current is outputted from thecorresponding output terminal O in accordance with the constant voltagevalue VGC applied to the gate G. That is, the respective constantcurrents necessary for the light emitting elements for R, G and B in thecolor organic EL panel 1 are outputted.

The output of the output constant current turns on/off in response tothe switching signal supplied from the external control unit (not shown)such as a controller.

The constant current control section 31 includes a constant currentcontrol section 31R for R, a constant current control section 31G for Gand a constant current control section 31B for B which output the gatevoltage VGC for R, G and B, for outputting a current necessary for thelight emitting elements for R, G and B from the constant current outputsection 30.

Those three constant current control sections 31 are identical instructure with each other except that the resistance values of theresistors RR, RG and RB for adjusting the value of the output voltage(the gate voltage VGC) are different from each other.

The output of the constant current control section 31R for R isconnected with the wiring terminal TR by a voltage wiring 32R for R. Therespective wiring terminals T are terminals used for measuring theoutput voltage of the respective constant current control sections 31 orfor testing the circuit state.

The voltage wiring 321R for R between the wiring terminal TR and theconstant current control section 31R for R is also connected to theconstant current output sections 301, 304, 307, . . . 30s−2 by the gatewiring 322R.

Similarly, the output of the constant current control section 31G for Gis connected with the wiring terminal TG by a voltage wiring 321G for Gand also connected to the constant current output sections 302, 305,308, . . . 30s−1 by the gate wiring 322G. Also, the output of theconstant current control section 31B for B is connected with the wiringterminal TB by a voltage wiring 321B for B and also connected to theconstant current output sections 303, 306, 309, . . . 30s by the gatewiring 322B.

As described above, the constant current control section 31R for R, theconstant current control section 31G for G and the constant currentcontrol section 31B for B are connected to every three constant currentoutput sections 301 to 30s by the voltage wiring 321R for R and the gatewiring 322R, the voltage wiring 321G for G and the gate wiring 322G, andthe voltage wiring 321B for B and the gate wiring 322B, respectively.With this structure, the constant current for R, the constant currentfor G and the constant current for B are outputted from the outputterminals O1 to Os arranged in a line or a plurality of lines in thearrangement order.

The structures of the constant current control section 31R for R, theconstant current control section 31G for G and the constant currentcontrol section 31B for B in FIG. 16 are structured in the same manneras those in the third embodiment mode of FIG. 12, but may be structuredin the same manner as those in any one of the above-described third tofifth embodiment modes.

Subsequently, a seventh embodiment mode will be described.

In the second embodiment mode, in the case where IC chips for aplurality of constant current output drivers are connected to the colororganic EL panel 1, adjustment can be made so that a difference in thecurrent supplied to both ends of the color organic EL panel 1 or adifference in the current value between end portions of the adjacentconstant current output driver ICs becomes small.

FIG. 17 shows a state in which a plurality of constant current outputdriver IC chips according to the sixth embodiment mode which wasdescribed with reference to FIG. 16 are connected, to the color organicEL panel 1, and the current values outputted from the respective outputterminals O.

As shown in FIG. 17(a), in the case where (s×n) anode terminals A existin the color organic EL panel 1, connection is made by using the nconstant current output drivers 3 (the number of output terminals O=s)of the first embodiment mode.

In this case, if the gate voltages VCG outputted to the respectiveconstant current output sections 301 to 30s from the respective constantvoltage output circuits 31R, 31G and 31B for R, G and B through thevoltage wirings 321R, 321G and 321B are varied within the respectiveconstant current output driver 3, the output current values from therespective constant current output sections 301 to 30s are varied.

Also, even if the gate voltages VCG are not varied, the outputtedcurrent values are varied within the chips due to the characteristicvariation of the FETs that constitute the respective constant currentoutput sections 301 to 30s.

As described above, the gate voltages VGC applied to the respectiveconstant current output sections 30 do not always have the same valuedepending on various conditions such as the wiring resistance of thevoltage wiring 321 or the gate wiring 322 but have voltage valuesslightly different due to a wiring distance or the like. The differencein the gate voltage VGC and the characteristic variation of therespective constant current output sections 30 cause a difference in thecurrent values outputted from the respective constant current outputsections 30 connected to the same voltage wiring 321 to the outputterminals O.

In FIG. 17(b), the axis of ordinate represents the current valuesoutputted from the respective constant current output sections 301, 304,. . . 30s−2 connected to the constant current control section 31 for Rby the voltage wiring 321R for R and the gate wiring 322R for R(accordingly, the current values outputted from the corresponding outputterminals O1, O4, . . . Os−2), and the axis of abscissa represents therespective constant current output sections 30 (or the respective outputterminals).

As shown in FIG. 17(b), because a difference between the adjacentconstant current output sections 301 and constant current output section304 connected to the same voltage wiring 321R is slight, a difference inthe current supplied to the adjacent organic ELs for R which areconnected to the same constant current output driver is also slight, anda difference in luminance between both the organic ELs cannot berecognized without any problems.

However, if being viewed from the whole one constant current outputdriver, there is a change in the current value having a constantinclination as a whole as indicated by arrows A1, A2 . . .

For that reason, there arises no problem if a change is made such thatthe constant current output section 301 and the constant current outputsection 30s−2 become substantially identical in output current value(for example, such a change that the current value goes up after it goesdown once). However, as shown in FIG. 17(b), if a constant or largerdifference exists in the output current value between both the outputterminals O1 and Os−2 (O2 and Os−1, O3 and Os), a large differenceoccurs in the current value between the constant current output drivers3 adjacently arranged as indicated by an arrow B in the figure. As aresult, because a difference in the currents that flow in the adjacentorganic ELs for R at a portion where the connected constant currentoutput driver changes is large, there is the possibility that thereoccurs a difference in luminance to the degree where the difference canbe recognized.

FIG. 17(c) shows the inclination of a current value when a difference inthe output current from the end portions of a plurality of constantcurrent output drivers 3 connected to each other is adjusted to besmall. In order to reduce the output current difference from the endportions, it is possible to adjust the value of the resistor R and toadjust the output voltage (the gate voltage VGC) of the constant currentcontrol section 31. In other words, when as indicated by an arrow A2′ inFIG. 17(c), the output current value (the left end value of A2′) fromthe first output terminal O1 of the second constant current outputdriver 3 from the left is made to lower, a difference in the currentvalue between the end portions of. the adjacent constant current outputdrivers can be reduced.

However, because the respective constant current output drivers 3 arebasically of the same structure, even if the output voltage of theconstant current control section 31 is changed, the tendency of theinclination (change) such as right down or right up with respect to thecurrent value shown in FIG. 17(b) is identical. That is, A2′ isdifferent in only the absolute value and the tendency of change isidentical with that of A2 and A1. For that reason, even if a differencein the current value between the constant current output drivers 3 issmall, there is the possibility that an evil influence occurs that alarge difference in the current value occurs between both ends, suchthat one end is bright whereas the other end is dark, when being viewedfrom the entire color organic EL panel 1 (or the entire plural constantcurrent output drivers) as shown in FIG. 17(c).

Under the above circumstances, in the seventh embodiment mode, not onlya voltage at the end portion on a side connected with the constantcurrent control section 31 of the constant current output driver isadjusted, but also a voltage between both the ends can be adjusted.

FIG. 18(a) shows the structure of the constant current output driver 3which is capable of adjusting the output current from both the ends ofthe constant current output sections 30 (that is, the output terminalsO) arranged in a line (or multiple stages) in the constant currentoutput driver.

As shown in FIG. 18, the constant current output driver includes twoconstant current control sections 31, respectively, that is, twoconstant current control sections for R 31R1 and 31R2, two constantcurrent control sections for G 31G1 and 31G2, and two constant currentcontrol sections for B 31B1 and 31B2 (hereinafter, representatively,referred to as “constant current control sections 311 and 312” both ofwhich are representatively referred to as “constant current controlsections 31”). Those six constant current control sections 31 as a wholeare identical in structure with that of the constant current controlsection 31 shown in FIG. 12 (the resistance values of the resistors Raredifferent from each other through adjustment, respectively).

Both the outputs of paired constant current control sections 311 areconnected to each other by the voltage wirings 321., and the voltagewirings 321 are connected to every three constant current outputsections 30 by the gate wirings 322 as in the sixth embodiment mode.

As described above, according to the seventh embodiment mode, the pairedtwo constant current control sections 311 and 312 are disposed for eachcolor of R, G and B, and both the constant current control sections 311and 312 are connected to each other by the voltage wiring 321, and thevoltage wirings 321 are connected to every three constant current outputsections 30 by the gate wirings 322. Accordingly, the inclination of therespective output current values in the arrangement direction of therespective constant current output sections 30 arranged in a line or thelike (or the respective output terminals O) can be adjusted at bothends.

With the above structure, if the constant current output driver 3 theoutput current values of which have the tendency of right down in thearrangement direction of the output terminal O as shown in FIG. 18(b),the current value outputted from the output terminal O1 (the constantcurrent output section 301) at the left end can be reduced as indicatedby an arrow à by increasing the output voltage (gate voltage VGC) of theconstant current control section for R 31R1 (decreasing the voltage VGSwith respect to VDD). Further, the current value outputted from theoutput terminal Os−2 (the constant current output section 30s−2) at theright end can be increased as indicated by an arrow A by decreasing theoutput voltage of the constant current control section for R 31R2(increasing the voltage VGS).

As described above, according to the seventh embodiment mode, becausethe output currents of the constant current output sections 30 (outputterminals 0) at both the ends can be adjusted by the paired constantcurrent control sections 311 and 312, for example, if a currentdifference between both the ends is Δi in the unadjusted state, theconstant current control section 31 at a side close to the outputterminal at which the current value is high is adjusted so that thecurrent value at a side where the current value is high is increased byΔi/2. Also, the constant current control section 31 at the opposite sideis adjusted so that the current value at a side where the current valueis low is increased by Δi/2. This makes it possible to prevent a changein luminance at both the ends of the adjacent constant current outputdrivers (refer to the arrow B in FIG. 17(b)) and a difference inbrightness at both the ends of the color organic EL panel 1 (refer toFIG. 17(c)) from occurring, even if a plurality of constant currentoutput drivers 3 are disposed.

Subsequently, an eighth embodiment mode will be described.

FIG. 19 shows the structure of the constant current output driver 3 inaccordance with the eighth embodiment mode.

According to the eighth embodiment mode, in the seventh embodiment modewhere the pair of constant current control sections 311 and 312 aredisposed for each of R, G and B, when the output current is adjusted bythe voltage adjustment of the respective constant current controlsections 311 and 312, the adjustment can be surely conducted.

In other words, as shown in FIG. 19, wiring resistances r are disposedat given intervals on the respective voltage wirings 321 that connectthe paired constant current control sections 311 and 312.

As usual, there is a case in which a protective resistor r0 is disposedbetween the wiring 321 and the constant current control section 31 inorder to prevent the influence due to static electricity in the outputof the constant current control section 31. Then, in the constantcurrent output driver 3 according to the seventh embodiment mode shownin FIG. 18, in the case of connecting the protective resistor r0, evenif the voltage is adjusted by the paired constant current controlsections 311 and 312, the amount of the adjusted voltage is used as avoltage drop in the protective resistor r0 with the result thatadjustment shown in FIG. 18(b) cannot be made.

That is, as shown in FIG. 19(b), even if the voltages of the constantcurrent control sections 311 and 312 are adjusted with respect to thecurrent (indicated by a dotted line) outputted from the output terminalO in the case where voltage is not adjusted, there is a case in whichthe unadjusted state indicated by the dotted line is substantially movedin parallel by the existence of the protective resistor r0. In thiscase, the effect of disposing a pair of constant current controlsections 31, respectively, is not obtained.

Under the above circumstance, in the eighth embodiment mode, as shown inFIG. 19(a), resistor components r are disposed on the wiring voltages321 between the respective gate wirings 322.

In this embodiment mode, the entire voltage wiring 311 connecting theconstant current control sections 311 an 312 are formed of polysiliconresistors, with the result that the resistor components r and theprotective resistors r0 are formed, respectively.

As described above, the amount of the voltage adjusted by the constantcurrent control sections 311 and 312 is used as the voltage drop of theentire voltage wiring including the protective resistors r0 at both theends with the arrangement of the resistor components r between therespective gate wirings 322. For that reason, as indicated by a solidline in FIG. 18(b), the inclination of the current value outputted fromthe respective output terminals O can be surely adjusted.

In the eighth embodiment mode, the entire voltage wiring 321 includingthe protective resistors r0 is formed of the polysilicon resistors.However, the voltage wiring 321 may be formed of the polysiliconresistor, and the protective resistor r0 may be additionally connectedto the voltage wiring 321.

Also, the resistor components r except for the polysilicon resistors maybe disposed on the voltage wirings 321. In this case, the resistorcomponents r may be disposed between the respective gate wirings 322 ordisposed at every predetermined intervals. As every given intervals, forexample, if the resistor component r is disposed between the gatewirings 322R of the constant current output section 301 and the constantcurrent output section 304, no resistor component r is disposed betweenthe gate wirings 322R of the constant current output section 304 and theconstant current output section 307, and the resistor component r isdisposed between the gate wirings 322R of the succeeding constantcurrent output section 307 and the succeeding constant current outputsection 3010. In this way, the resistor components r may be disposed atevery two intervals. Also, the resistor components r may be disposed atevery arbitrary selected number intervals such as every three intervals,every four intervals, every five intervals or every eleven intervals. Inaddition, the resistor components r may be disposed at one location inthe center between the paired constant current control section 311 andconstant current control section 312, at two locations of the trisectionthereof or at three locations of the quadsection thereof.

Subsequently, a ninth embodiment mode will be described.

In the ninth embodiment mode, the constant current output driver 3 isformed of the different IC chips of a constant current output device 300having s constant current output sections 30 and a constant currentcontrol unit 31 having three constant current control section 310.

FIG. 20 shows a constant current output device 300(a) and a constantcurrent control unit 310 (b) of the constant current output driver 3 inthe ninth embodiment mode.

As shown in FIG. 20(a), the constant current output device 300 includesa pair of wiring terminals TR, a pair of wiring terminals TG and a pairof wiring terminals TB, that is the six wiring terminals TR1 and TR2,TG1 and TG2, and TB1 and TB2 in total (representatively referred to as“T1 and T2”) The respective paired wiring terminals T1 and T2 areconnected to each other by the voltage wirings 321, and the voltagewirings 321 are connected with every three constant current outputsections 30 by the gate wirings 322.

On the other hand, as shown in FIG. 20(b), the constant current controlunit 310 includes a constant current control section for R 31R, aconstant current control section for G 31G and a constant currentcontrol section for B 31B, and the respective constant current controlsections 31 are connected with the wiring terminals TR0 and TG0 and TGB,respectively.

FIG. 21 shows a state in which the constant current output device 300and the constant current control unit 310 are connected to each other inthe ninth embodiment mode.

As shown in the figure, the color organic EL panel 1 having u anodeterminals A1 to Au (TR1 and TR2, TG1 and TG2, TB1 and TB2) are connectedwith q constant current output devices 300 a, 300 b, . . . 300 q.

Then, in the adjacently disposed constant current output devices 300,the wiring terminal TR2 and the wiring terminal TR1 are connected toeach other, the wiring terminal TG2 and the wiring terminal TG1 areconnected to each other, and the wiring terminal TB2 and the wiringterminal TB1 are connected to each other.

On the other hand, out of the constant current output devices 300disposed at both the ends, the wiring terminals TR1, TG1 and TB1 of theconstant current output device 300 a are connected to the wiringterminals TR0, TG0 and TB0 of the constant current control unit 310 a,respectively, and the wiring terminals TR2, TG2 and TB2 of the constantcurrent output device 300 b are connected to the wiring terminals TR0,TG0 and TB0 of the constant current control unit 310 b, respectively.

As described above, according to this embodiment mode, since theconstant current output driver 3 is made up of the separate elements ofthe constant current output device 300 and the constant current controlunit 310, the voltage wirings 321 of the plural constant current outputdevices 300 can be continuously connected to each other, and theconstant current output driver 3 can be structured by using at least oneof the constant current control units 310 (a case in which the constantcurrent control unit 310 b is not connected in FIG. 21), thereby makingit possible to reduce the number of the constant current controlsections 31.

The above description was given of a case in which all the voltagewirings 321 of q constant current output devices 300 are connected.However, the plural voltage wirings 321 as one unit may be connected toeach other, and the constant current output devices 300 may beconnected. For example, q constant current output devices 300 is dividedinto two groups each having q/2 constant current output devices 300, andthe adjacent q/2 voltage wirings 321 are connected to each other, andthe constant current output devices 300 at both ends or one end areconnected with the constant current control unit 310.

Also, in the voltage wirings 321 according to the ninth embodiment mode,the entire voltage wirings 321 are formed of the polysilicon resistorsas in the eighth embodiment mode, or the resistor components r may bedisposed partially.

In the above-described sixth to ninth embodiments, the respectiveconstant current output sections 301 to 30s are made identical instructure, and the respective constant current control sections 31R, 31Gand 31B are made identical in structure except for the values of theresistors RR, GG and BB, as the result of which the structure within thechip is simplified to make manufacturing easy.

However, it is presumed that appropriate current values for R, G and Bare not obtained depending on the kind of the connected organic EL panel1 or a demand on control. In this case, the constant current outputsections for R 301, 304, . . . 30(s−2) may be made identical instructure, the constant current output sections for G 302, 305, . . .30(s−1) may be made identical in structure, and the constant currentoutput sections for B 303, 306, . . . 30s may be made identical instructure. Also, the structure of the respective constant currentcontrol sections 31R, 31G and 31B are adapted to the correspondingconstant current output sections 30 for R, G and B. In this case, theconstant current FET 51 of the constant current control section for R31R and the constant current FET for R 50 are formed of elements havingthe same temperature characteristic, the constant current FET 51 of theconstant current control section for G 31G and the constant current FETfor G 50 are formed of elements having the same temperaturecharacteristic, and the constant current FET 51 of the constant currentcontrol section for B 31B and the constant current FET for B 50 areformed of elements having the same temperature characteristic.

According to the present invention, since the switching element isdisposed between the power supply and the constant current elementwithout the switching element being disposed between the constantcurrent output element and the output terminal, over-shoot occurring inthe current outputted from the output terminal can be suppressed.

Also, since the FET that applies a constant voltage to the gate isdisposed between the constant current output element and the outputterminal, a change of the output constant current value depending on thevoltage can be reduced, and a variation of the constant current valuedue to switching can also be suppressed.

Further, the constant current output driver is structured by: an outputterminal; a first field effect transistor connected between the outputterminal and a power supply, for outputting a constant current with theapplication of a constant voltage to a gate thereof; switching meansconnected between the first field effect transistor and the outputterminal or the power supply, for electrically connecting ordisconnecting the first field effect transistor and the output terminalor the power supply; and a constant voltage applying circuit having atemperature characteristic which changes in the same manner as thetemperature characteristic of the first field effect transistor, forapplying a constant voltage to the first field effect transistor at aconstant temperature. With this structure, a change of the outputcurrent due to the temperature can be reduced.

Still further, the constant current output driver is structured by: aplurality of output terminals; field effect transistors the number ofwhich is equal to that of the output terminals, which are connectedbetween the output terminals and a power supply and which output aconstant current with the application of a given voltage to gatesthereof; switching means for electrically connecting and disconnectingthe respective field effect transistors and the respective outputterminals or the power supply, independently; a first constant currentcontrol section that generates a first voltage; a second constantcurrent control section that generates a second voltage; a thirdconstant current control section that generates a third voltage; a firstwiring that connects an output of the first constant current controlsection to every three gates of the plurality of field effecttransistors; a second wiring that connects an output of the secondconstant current control section to the gates of the respective fieldeffect transistors adjacent to the respective field effect transistorsto which the first wiring is connected; and a third wiring that connectsan output of the third constant current control section to the gates ofthe respective field effect transistors further adjacent to therespective field effect transistors to which the second wiring isconnected. With this structure, connection to the light emitting elementpanel for color display can be made by a single-layer wiring.

What is claimed is:
 1. A constant current output driver for emitting alight from a light emitting element by supplying a constant current, theconstant current output driver comprising: a constant current outputelement that outputs a constant current; a first switching elementdisposed between the constant current output element and a power supplyfor electrically connecting and disconnecting the power supply and theconstant current output element; and a first output terminal connectedto a current output side of the constant current output element with noswitching element disposed therebetween.
 2. A constant current outputdriver for emitting a light from a light emitting element by supplying aconstant current, the constant current output driver comprising: aconstant current output element that outputs a constant current; a firstswitching element disposed between the constant current output elementand a power supply for electrically connecting and disconnecting thepower supply and the constant current output element; a second switchingelement connected between a current output side of the constant currentoutput element and a second terminal for performing an on/off operationin association with the on/off operation performed by the firstswitching element; and a first output terminal connected between thecurrent output side of the constant current output element and thesecond switching element with no switching element disposedtherebetween.
 3. A constant current output driver comprising: a firstfield effect transistor for outputting a constant current in response tothe application of a constant voltage to a gate thereof; a second fieldeffect transistor disposed between the first field effect transistor anda power supply for electrically connecting and disconnecting the powersupply and the first field effect transistor; and a first outputterminal connected to a current output side of the first field effecttransistor with no switching element being disposed between the firstoutput terminal and the current output side of the first field effecttransistor.
 4. A constant current output driver comprising: a firstfield effect transistor for outputting a constant current in response tothe application of a constant voltage to a gate thereof; a second fieldeffect transistor disposed between the first field effect transistor anda power supply for electrically connecting and disconnecting the powersupply and the first field effect transistor; a third field effecttransistor connected in series with a current output side of the firstfield effect transistor and having a gate applied with a constantvoltage different from the constant voltage which is applied to the gateof the first field effect transistor; and a first output terminalconnected to a current output side of the third field effect transistorwith no switching element disposed therebetween.
 5. A constant currentoutput driver comprising: a first field effect transistor for outputtinga constant current in response to the application of a constant voltageto a gate thereof; a second field effect transistor disposed between thefirst field effect transistor and a power supply for electricallyconnecting and disconnecting the power supply and the first field effecttransistor; a third field effect transistor having a channel regiondifferent from that of the second field effect transistor and beingconnected between a current output side of the first field effecttransistor and a second terminal, the third field effect transistorhaving a gate commonly connected to an input terminal together with agate of the second field effect transistor; and a first output terminalconnected between a current output side of the first field effecttransistor and the third field effect transistor with no switchingelement disposed therebetween.
 6. A constant current output drivercomprising: a first field effect transistor for outputting a constantcurrent in response to the application of a constant voltage to a gatethereof; a second field effect transistor disposed between the firstfield effect transistor and a power supply for electrically connectingand disconnecting the power supply and the first field effecttransistor; a third field effect transistor connected in series with acurrent output side of the first field effect transistor and having agate supplied with a constant voltage different from the constantvoltage which is applied to the gate of the first field effecttransistor; a fourth field effect transistor having a channel regiondifferent from that of the second field effect transistor, connectedbetween a current output side of the third field effect transistor and asecond terminal, and having a gate commonly connected to an inputterminal together with a gate of the second field effect transistor; anda first output terminal connected between the current output side of thethird field effect transistor and the fourth field effect transistorwith no switching element disposed therebetween.
 7. A constant currentoutput driver comprising: a first field effect transistor connected to apower supply for outputting a constant current in response to theapplication of a constant voltage to a gate thereof; a second fieldeffect transistor connected in series with a current output side of thefirst field effect transistor for conducting a switching operation; athird field effect transistor connected in series with a current outputside of the second field effect transistor and having a gate suppliedwith a constant voltage different from the constant voltage which isapplied to the gate of the first field effect transistor; a fourth fieldeffect transistor having a channel region different from that of thesecond field effect transistor, connected between a current output sideof the third field effect transistor and a second terminal, and having agate commonly connected to an input terminal together with a gate of thesecond field effect transistor; and a first output terminal connectedbetween the current output side of the third field effect transistor andthe fourth field effect transistor with no switching element disposedtherebetween.
 8. A constant current output driver comprising: a firstfield effect transistor connected to a power supply for outputting aconstant current in response to the application of a constant voltage toa gate thereof; a second field effect transistor connected in serieswith a current output side of the first field effect transistor andhaving a gate supplied with a constant voltage different from theconstant voltage which is applied to the gate of the first field effecttransistor; a third field effect transistor connected in series with acurrent output side of the second field effect transistor for conductinga switching operation; a fourth field effect transistor having a channelregion different from that of the third field effect transistor,connected between a current output side of the third field effecttransistor and a second terminal, and having a gate commonly connectedto an input terminal together with a gate of the second field effecttransistor; and a first output terminal connected between the currentoutput side of the third field effect transistor and the fourth fieldeffect transistor with no switching element disposed therebetween.
 9. Aconstant current output driver comprising: an output terminal; a firstfield effect transistor connected between the output terminal and apower supply for outputting a constant current in response to theapplication of a constant voltage to a gate thereof; switching meansconnected between the first field effect transistor and one of theoutput terminal or the power supply for electrically connecting anddisconnecting the first field effect transistor and one of the outputterminal or the power supply; and a constant voltage applying circuithaving a temperature characteristic which changes in the same manner asthe temperature characteristic of the first field effect transistor forapplying a constant voltage to the first field effect transistor at aconstant temperature.
 10. A constant current output driver according toclaim 1; further comprising a constant voltage applying circuitcomprised of voltage dividing resistor means for dividing an inputvoltage, and a second field effect transistor connected in serialbetween the voltage dividing resistor means and the power supply andhaving a gate connected in a saturated state; wherein the firstswitching element comprises a first field effect transistor and a gateof the second field effect transistor is connected to a gate of thefirst field effect transistor.
 11. A constant current output driveraccording to claim 2; wherein the first switching element comprises afirst field effect transistor having a gate which inputs a switchingsignal and the second switching element comprises a second field effecttransistor; and further comprising a third field effect transistor whichhas a gate connected to ground and which is also connected to one of apower supply side or the second field effect transistor at a connectionposition of the first field effect transistor.
 12. A constant currentoutput driver according to claim 2; wherein the first and secondswitching elements comprise a first field effect transistor and a secondfield effect transistor formed of the same standard elements.
 13. Aconstant current output driver according to claim 10; wherein thevoltage dividing resistor means comprises one of the combination of aresistor ladder, a variable resistor, and a terminal to which a resistoris externally attached, or a resistor and a terminal to which anotherresistor is externally attached connected in parallel to the terminal.14. A constant current output driver according to any one of claims 3 to6; further comprising a voltage follower circuit; wherein a gate of thesecond field effect transistor is connected to an input of the voltagefollower circuit, and an output of the voltage follower circuit isconnected to a gate of the first field effect transistor.
 15. A constantcurrent output driver integrated circuit comprising: a first pluralityof output terminals; a first plurality of field effect transistors eachconnected between a respective output terminal and a power supply foroutputting a constant current in response to the application of a givenvoltage to a gate thereof; switching means for electrically connectingand disconnecting the respective field effect transistors and one of therespective output terminals or the power supply, independently; a firstconstant current control section for generating a first voltage; asecond constant current control section for generating a second voltage;a third constant current control section for generating a third voltage;a first wiring pattern for connecting an output of the first constantcurrent control section to a gate of every third one of the firstplurality of field effect transistors; a second wiring pattern forconnecting an output of the second constant current control section togates of respective field effect transistor transistors adjacent to therespective field effect transistors to which the first wiring pattern isconnected; and a third wiring pattern for connecting an output of thethird constant current control section to gates of respective fieldeffect transistors further adjacent to the respective field effecttransistors to which the second wiring pattern is connected.
 16. Aconstant current output driver according to claim 15; wherein the numberof the output terminals and the number of the field effect transistorsis 192, respectively.
 17. A constant current output driver according toeither one of claim 15 or 16; further comprising a first wiring terminalto which the first wiring pattern is connected, a second wiring terminalto which the second wiring pattern is connected, and a third wiringterminal to which the third wiring pattern is connected.
 18. A constantcurrent output driver according to either one of claim 15 or 16; furthercomprising another first constant current control section, anothersecond constant current control section, and another third constantcurrent control section; wherein the first wiring pattern includes afirst voltage wiring pattern that connects outputs of both firstconstant current control sections to each other, and a first gate wiringpattern that connects the first voltage wiring pattern and therespective gates; wherein the second wiring pattern includes a secondvoltage wiring that connects outputs of both second constant currentcontrol sections to each other, and a second gate wiring pattern thatconnects the second voltage wiring pattern and the respective gates; andwherein the third wiring pattern includes a third voltage wiring patternthat connects outputs of both third constant current control sections toeach other, and a third gate wiring pattern that connects the thirdvoltage wiring pattern and the respective gates.
 19. A constant currentoutput driver according to claim 18; further comprising a resistordisposed on the voltage wiring pattern between at least one pair of gatewiring patterns.
 20. A constant current output driver according to claim18; wherein the voltage wiring is formed of a polysilicon resistor. 21.A constant current output driver integrated circuit comprising: a firstplurality of output terminals; a first plurality of field effecttransistors each connected between a respective output terminal and apower supply for outputting a constant current in response to theapplication of a given voltage to a gate thereof; switching means forelectrically connecting and disconnecting the respective field effecttransistors and one of the respective output terminals or the powersupply, independently; first, second and third voltage input terminalsto which an input voltage is applied; first, second and third voltageoutput terminals from which the input voltage is output; a first voltagewiring pattern for connecting the first voltage input terminal and thefirst voltage output terminal; a second voltage wiring pattern forconnecting the second voltage input terminal and the second voltageoutput terminal; a third voltage wiring pattern for connecting the thirdvoltage input terminal and the third voltage output terminal; a firstgate wiring pattern for connecting the first voltage wiring pattern to agate of every third one of the first plurality of field effecttransistors; a second gate wiring pattern for connecting the secondvoltage wiring pattern to gates of respective field effect transistorsadjacent to the respective field effect transistors to which the firstwiring pattern is connected; and a third gate wiring pattern forconnecting the third voltage wiring pattern to gates of respective fieldeffect transistors further adjacent to the respective field effecttransistors to which the second wiring pattern is connected.